Sheet storage device and image forming unit therewith

ABSTRACT

A sheet storage device includes a housing, a sheet stacking tray, a shaft, a first pulley, a second pulley, a plurality of wires, and a driving device. The driving device includes a drive portion and a drive transfer portion. The sheet stacking tray ascends as a driving-side coupling rotates in a forward direction, and descends as the driving-side coupling rotates in a reverse direction. When a driven-side coupling stops rotating in the reverse direction, the driving-side coupling rotates idly relative to the driven-side coupling.

INCORPORATION BY REFERENCE

This application is based on and claims the benefit of priority from Japanese Patent Application No. 2021-023842 filed on Feb. 18, 2021, the contents of which are hereby incorporated by reference.

BACKGROUND

The present disclosure relates to a sheet storage device, and relates also to an image forming unit provided with a sheet storage device.

With image forming apparatuses such as copiers, printers, and facsimile machines, in a situation where a single image forming apparatus is shared by a large number of users, increased quantities of sheets (recording media such as printing paper sheets and envelopes) are consumed per image forming apparatus. In general, an image forming apparatus can only store several hundred sheets inside its body, and thus needs to be replenished with sheets frequently. As a remedy, a large-capacity sheet storage device is known that is capable of storing several thousand sheets and that is attached to a side face of an image forming apparatus so that sheets are supplied from the sheet storage device to the image forming apparatus.

Such a sheet storage device includes a sheet stacking tray on which sheets are stacked, a pulley portion that is supported so as to be rotatable in forward and reverse directions, a driving device that is coupled to the pulley portion to rotate it, and a wire of which one end is fixed to the pulley portion and of which the other end is fixed to the sheet stacking tray. The pulley portion can wind up the wire in such a way that the wire is wound around the outer circumferential surface of the pulley portion. As the pulley portion rotates in the forward direction, the wire is wound around the pulley portion. As the pulley portion rotates in the reverse direction, the wire wound around the pulley portion is unwound from the pulley portion. As the wire is wound up, the sheet stacking tray ascends. When the sheet stacking tray descends, the wire is unwound from the pulley portion.

In the sheet storage device mentioned above, the driving device rotates the pulley portion in accordance with the remaining quantity of sheets stacked on the sheet stacking tray, and the wire is wound and unwound to raise and lower the sheet stacking tray. Specifically, as the remaining quantity of sheets decreases, the driving device applies a rotational driving force in the forward direction (wire winding direction) to the pulley portion to make it rotate in the forward direction. This causes the wire to be wound around the pulley portion and the sheet stacking tray to ascend. For sheet replenishment, the user pushes down the sheet stacking tray by hand, or a rotational driving force in the reverse direction (wire unwinding direction) is applied from the driving device to the pulley portion to rotate the pulley portion in the reverse direction and thereby lower the sheet stacking tray, so that the user can place sheets P on the sheet stacking tray thus lowered.

Over the sheet stacking tray, there is provided a sheet feed device that feeds sheets to the image forming apparatus. The sheet feed device includes a pickup roller that is disposed opposite the sheets on the sheet stacking tray in the up-down direction. As mentioned above, the sheet storage device raises and lowers the sheet stacking tray in accordance with the remaining quantity of sheets to keep the top surface of the sheets at a fixed height so that, at this height, the outer circumferential surface of the pickup roller makes contact with the top surface of the sheet. As the pickup roller rotates, the sheet in contact with it is conveyed downstream in the feeding direction.

Some sheet storage devices like the one mentioned above include a detection sensor and a controlling means. The detection sensor detects the position of the sheet stacking tray in the up-down direction. Based on the results of detection by the detection sensor, the controlling means controls the driving device such that, when the sheet stacking tray lowers to its lowest position (when the wire is fully unwound), the driving device does not transmit the rotational driving force in the reverse direction (unwinding direction) to the pulley portion.

Also known is a sheet storage device in which, in an end part of the pulley portion in its rotation axis direction, a cut portion is formed that is cut in the axial direction so that one end of the wire is fixed to the end part of the pulley portion in its rotation axis direction. In a downstream part of the cut portion with respect to the forward rotation direction, an inclined portion is formed. In an upstream part of the cut portion with respect to the forward rotation direction, a recessed portion is formed that is recessed in the reverse rotation direction.

On this sheet storage device, as the pulley portion rotates in the forward direction (wire winding direction), the wire is caught in the recessed portion of the cut portion. This causes the wire in a stage engaged with the cut portion to be wound around the pulley portion. As the pulley portion rotates in the reverse direction, the wire is unwound, and when the wire is fully unwound from the pulley portion, the wire comes out of the recessed portion. In this state, as the pulley portion rotates further in the reverse direction, the wire moves along the inclined portion out of the cut portion, and the wire disengages from the cut portion. In this state, as a suspending portion rotates further in the reverse direction, although the wire cyclically makes contact with the inclined portion, it is guided out of the cut portion by the inclined portion so as not to engage with the cut portion.

SUMMARY

According to one aspect of the present disclosure, a sheet storage device includes a housing, a sheet stacking tray, a shaft, a first pulley, a second pulley, a plurality of wires, and a driving device. The sheet stacking tray is supported inside the housing so as to be ascendable and descendable, and on the sheet stacking tray, sheets are stacked. The shaft extends in the width direction of the housing, and is supported so as to be rotatable in forward and reverse directions. The first pulley is fixed to one end of the shaft. The second pulley is fixed to another end part of the shaft. The plurality of wires suspending the sheet stacking tray. The plurality of wires wound around the first and second pulleys as the shaft rotates in the forward direction. The plurality of wires unwound from the first and second pulleys as the shaft rotates in the reverse direction. The driving device includes a drive portion that generates a rotational driving force and

a drive transfer portion that transmits the rotational driving force in the forward direction to the first pulley and that shuts off the rotational driving force in a reverse direction. The drive transfer portion includes a driving-side coupling that is provided on the drive shaft of the drive portion so as to rotate together with the drive shaft and that rotates together with the drive shaft and a driven-side coupling that is provided on the first pulley so as to rotate together with the first pulley and that is coupled to the driving-side coupling. When, with the rotational driving force in the forward direction, the driving-side coupling rotates in the forward direction, the driving-side coupling and the driven-side coupling couple to each other to transmit the rotational driving force in the forward direction from the drive portion, so that the first and second pulley rotates in the forward direction with the shaft, so that the plurality of wires are wound around the first and second pulleys to lift up the sheet stacking tray. When with the rotational driving force in the reverse direction, the driving-side coupling rotates in the reverse direction, the driven-side coupling with uncoupled state, by following the rotation of the driving-side coupling in the reverse direction, rotate in the reverse direction, due to the weight of the sheet stacking tray, the plurality of wires are unwound from the first pulley and the sheet stacking tray descends. when the sheet stacking tray stops descending and the driven-side coupling stops rotating in the reverse direction while the driving-side coupling is rotating in the reverse direction, the driving-side coupling rotates idly relative to the driven-side coupling that has stopped.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an outline sectional view showing an outline of the construction of an image forming unit that includes a sheet storage device according to an embodiment of the present disclosure and an image forming apparatus;

FIG. 2 is a perspective view showing the structure inside a housing of the sheet storage device;

FIG. 3 is a plan view of a pulley portion and around a driving device as seen from above in FIG. 2;

FIG. 4 is a perspective view of a first pulley and a drive transmission portion;

FIG. 5 is a plan view of the first pulley as seen from outward of it in the axial direction (from the driving device side) as the first pulley is rotating in the forward direction (counter-clockwise in the illustration);

FIG. 6 is a plan view of the first pulley as seen from outward of it in the axial direction (from the driving device side) as the first pulley is rotating in the reverse direction (clockwise in the illustration);

FIG. 7 is a plan view showing a state where, with a sheet stacking tray lowered to the lowest position in the ascent-descent direction, the drive portion is applying a rotational driving force in the reverse direction (direction indicated by arrow C2 in the illustration) to the second claw portion; and

FIG. 8 is a side view showing a reference example of a wire winding mechanism in a conventional sheet storage device.

DETAILED DESCRIPTION

With reference to the accompanying drawings, a description will be given below of a sheet storage device 20 according to an embodiment of the present disclosure and an image forming unit 100 that includes the sheet storage device 20.

FIG. 1 is an outline sectional view showing an outline of the construction of the image forming unit 100 that includes the sheet storage device 20 according to the embodiment of the present disclosure and an image forming apparatus 1. The image forming apparatus 1 includes a sheet feed portion 2, a sheet conveyance portion 3, an image forming portion 4, a fixing device 5, and an image reading portion 6. The sheet feed portion 2 is disposed in a lower part of the image forming apparatus 1. The sheet conveyance portion 3 is disposed by the side of the sheet feed portion 2. The image forming portion 4 is disposed over the sheet conveyance portion 3. The fixing device 5 is disposed on the discharge side of the image forming portion 4. The image reading portion 6 is disposed over the image forming portion 4 and the fixing device 5.

The sheet feed portion 2 includes a plurality of sheet feed cassettes 7 that store sheets P of plain paper. As a sheet feed roller 8 rotates, the sheet feed portion 2 feeds out the sheets P one by one reliably from a selected one of the plurality of sheet feed cassettes 7.

A hand feed tray 25 is for stacking, and for feeding out to the sheet conveyance portion 3, sheets of pain paper of a size different from the sizes of the sheets P stored in the sheet feed cassettes 7, or OHP sheets, or sheets like envelopes.

A sheet P fed to the sheet conveyance portion 3 is conveyed through a sheet feed passage 10 toward the image forming portion 4. The sheet feed passage 10 extends upward from the sheet feed cassettes 7, and midway meets a confluence passage 52 that is connected to a sheet discharge port 51 (described later) of the sheet storage device 20.

The image forming portion 4 forms a toner image on a sheet P by a electrophotographic process. The image forming portion 4 includes a photosensitive member 11 pivoted so as to be rotatable in the direction indicated by an arrow in FIG. 1, and further includes, around the photosensitive member 11 along its rotation direction, a charging portion 12, an exposure portion 13, a developing device 14, a transfer portion 15, a cleaning portion 16, and a destaticizing portion 17.

The charging portion 12 includes a charging wire supplied with a high voltage. When through corona discharge from this charging wire a predetermined potential is applied to the surface of the photosensitive member 11, the surface of the photosensitive member 11 is electrostatically charged uniformly. When light based on the image data of a document read by the image reading portion 6 is shone on the photosensitive member 11 from the exposure portion 13, the surface potential on the photosensitive member 11 is attenuated selectively from place to place, so that an electrostatic latent image is formed on the surface of the photosensitive member 11.

The developing device 14 then develops the electrostatic latent image on the surface of the photosensitive member 11, so that a toner image is formed on the surface of the photosensitive member 11. The toner image is transferred by the transfer portion 15 to the sheet P fed to between the photosensitive member 11 and the transfer portion 15.

The sheet P having the toner image transferred to it is conveyed toward the fixing device 5, which is disposed downstream of the image forming portion 4 in the sheet conveyance direction. In the fixing device 5, the sheet P is heated and pressed by a heating roller 18 (heating member) and a pressing roller 18 (pressing member), so that the toner image is fused to be fixed to the sheet P. The sheet P having the toner image fixed to it is then discharged onto a discharge tray 21 by a pair of discharge rollers 22.

After the transfer in the transfer portion 15, the toner remaining on the surface of the photosensitive member 11 is removed by the cleaning portion 16, and the electric charge remaining on the surface of the photosensitive member 11 is eliminated by the destaticizing portion 17. The photosensitive member 11 is then electrostatically charged again by the charging portion 12, so that image formation continues in a similar manner.

By the side of the image forming apparatus 1, adjacent to it, there is disposed a large-capacity sheet storage device 20 that can store several thousand sheets P. The sheet storage device 20 includes, inside a housing 26 that forms the body of the sheet storage device 20, a sheet stacking tray 27, a suspending member 60, a wire 29, a driving device 30, and a sheet feed device 32. The housing 26 is formed substantially in the shape of a rectangular parallelepiped. To the bottom surface of the housing 26, a plurality of casters 24 are fitted to allow easy transport of the sheet storage device 20.

FIG. 2 is a perspective view showing the structure inside the housing 26 of the sheet storage device 20. The far right side surface of the housing 26 in FIG. 2 corresponds to the front side surface in FIG. 1 with respect to its plane. The left side surface of the housing 26 in FIG. 2 corresponds to the rear side surface in FIG. 1 with respect to its plane. The width direction of the sheets P stored in the sheet storage device 20 points in the same direction as the direction from the front to the rear of the housing 26.

As shown in FIG. 2, the sheet stacking tray 27 includes a tray portion 33, which is a plate-shaped member extending parallel to the horizontal plane, and fixture portions 34, which protrude from the four corners of the tray portion 33 outward in its width direction (the width direction of the sheets P). The sheet stacking tray 27 is supported inside the housing 26 so as to be ascendable and descendable along the up-down direction (direction indicated by arrow Y in FIG. 2). The sheets P are stacked on the tray portion 33.

The suspending member 60 suspends the sheet stacking tray 27 across the wire 29 in such a way that the sheet stacking tray 27 is ascendable and descendable inside the housing 26. Here, the wire 29 includes four wires, namely a first wire 29 a, a second wire 29 b, a third wire 29 c, and a fourth wire 29 d. The suspending member 60 includes a shaft 35, a pulley portion 28 (a first pulley 36 and a second pulley 37), and sheaves 41 a, 41 b, 41 c, and 41 d.

The shaft 35 extends in a horizontal direction (the width direction of the sheets P) perpendicular to the ascent-descent direction of the sheet stacking tray 27. The sheet shaft 35 is supported inside the housing 26 so as to be rotatable in forward and reverse directions (clockwise and counter-clockwise in FIG. 1). To the opposite ends of the shaft 35 with respect to the direction along its rotation axis, the pulley portion 28 (the first and second pulleys 36 and 37) is fitted. The pulley portion 28 will be described in detail later.

As shown in FIG. 2, the pulley portion 28 includes the first and second pulleys 36 and 37. The first and second pulleys 36 and 37 are supported so as to be rotatable in forward and reverse directions. The first pulley 36 is attached to one end part of the shaft 35 (here, a part of it located at the rear side of the image forming apparatus 1). The second pulley 37 is attached to an other end part of the shaft 35 (here, a part of it located at the front side of the image forming apparatus 1). The first and second pulleys 36 and 37 and the shaft 35 are disposed coaxially. The first and second pulleys 36 and 37 are identically shaped and identically structured; accordingly, the following description deals only with the first pulley 36, and no overlapping description will be given of the second pulley 37.

FIG. 3 is a plan view of the suspending member 60 and around the driving device 30 as seen from above in FIG. 2. FIG. 4 is a perspective view of the first pulley 36 and a drive transmission portion 31. In the following description, of the directions of the rotation of the pulley portion 28 and of the rotational driving force of the driving device, the direction in which the wire 29 is wound around the pulley portion 28 is referred to as the “forward direction” (direction indicated by arrow C1 in the illustration), and the direction in which the wire 29 is unwound from the pulley portion 28 is referred to as the “reverse direction” (direction indicated by arrow C2 in the illustration).

As shown in FIGS. 3 and 4, the first pulley 36 has a winding portion 38, which is located in the middle of the first pulley 36 in the axial direction, and flange portions 39 a to 39 c, which are located in the middle of the first pulley 36 in the axial direction and which divide the winding portion 38 into two parts in the axial direction.

The winding portion 38 winds up the wire 29 in such a way that the wire 29 is wound around the outer circumferential surface of the first pulley 36. The winding portion 38 has a tapered outer diameter that increases toward one side in the axial direction (inward in the axial direction). As mentioned above, the winding portion 38 is divided by the flange portions 39 a to 39 c into two parts, namely a first winding portion 38 a and a second winding portion 38 b. In the first and second winding portions 38 a and 38 b of the first pulley 36 respectively, the first and second wires 29 a and 29 b of the wire 29 can be wound up. In the first and second winding portions 38 a and 38 b of the second pulley 37 respectively, the third and fourth wires 29 c and 29 d can be wound up.

The flange portion 39 a, which is located in an end part of the first winding portion 38 a, and the flange portion 39 b, which is located in an end part of the second winding portion 38 b, each have a cut portion 40 formed in it. With the cut portion 40 in the flange portion 39 a, an end part of the first wire 29 a can engage. With the cut portion 40 in the flange portion 39 b, an end part of the second wire 29 b can engage. In an end part of each of the first and second wires 29 a and 29 b, a locking portion (not shown) is formed that has the shape of a sphere with a diameter greater than the diameter of the wire 29. Hooking the locking portion in the cut portion 40 permits the first and second wires 29 a and 29 b to engage with the first pulley 36.

As the first pulley 36 rotates, the first and second wires 29 a and 29 b are wound and unwound. As the second pulley 37 rotates, the third and fourth wires 29 c and 29 d are wound and unwound.

Referring back to FIGS. 1 and 2, the wires 29 (first, third, second, and fourth wires 29 a, 29 c, 29 b, and 29 d) have one ends fixed to the pulley portion 28 and the other ends fixed to the fixture portions 34, so as to suspend the sheet stacking tray 27 from the pulley portion 28 via the plurality of (here, four) sheaves 41 a to 41 d. The sheaves 41 a and 41 b are disposed at the rear side of the housing 26, and the sheaves 41 c and 41 d are disposed at the front side of the housing 26.

The other end of the first wire 29 a (its end opposite from its end fixed to the first pulley 36) and the other end of the second wire 29 b are fixed to the fixture portions 34 located at the rear side of the housing 26. The other end of the first wire 29 a is fixed to that fixture portion 34 which is located closer to the pulley portion 28 (farther from the image forming apparatus 1) than the other end of the second wire 29 b.

The other end of the third wire 29 c and the other end of the fourth wire 29 d are fixed to the fixture portions 34 located at the front side of the housing 26. The other end of the third wire 29 c is fixed to that fixture portion 34 which is located closer to the pulley portion 28 (farther from the image forming apparatus 1) than the other end of the fourth wire 29 d.

The sheaves 41 a to 41 d are rotatably supported above the pulley portion 28 (see FIG. 2). The first and second wires 29 a and 29 b extend from the first pulley 36 upward to be hooked on the sheave 41 a. The first wire 29 a extends from the pulley wheel 41 a vertically downward to suspend the sheet stacking tray 27. The second wire 29 b extends from the sheave 41 a horizontally upstream in the sheet conveyance direction to be hooked on the sheave 41 b, which is located farther from the pulley portion 28 than the sheave 41 a, and extends from the sheave 41 b vertically downward to suspend the sheet stacking tray 27.

The third and fourth wires 29 c and 29 d extend from the second pulley 37 upward to be hooked on the sheave 41 c. The third wire 29 c extends from the sheave 41 c vertically downward to suspend the sheet stacking tray 27. The fourth wire 29 d extends from the sheave 41 c horizontally upstream in the sheet conveyance direction to be hooked on the sheave 41 d, which is located farther from the pulley portion 28 than the sheave 41 c, and extends from the sheave 41 d vertically downward to suspend the sheet stacking tray 27.

With the weight of the sheet stacking tray 27 and the sheets P, the wires 29 apply to the suspending member 60 a suspension load, which is a load acting vertically downward. The suspension load via the sheaves 41 a to 41 d acts as a rotational force that rotates the pulley portion 28 (first and second pulleys 36 and 37) in the reverse direction. It is assumed that, when the user presses down the sheet stacking tray 27, the pressing force adds to the suspension load.

As shown in FIG. 3, outward of the first pulley 36 in the axial direction (at the side opposite from the second pulley block 37), the driving device 30 is disposed that can apply a rotational driving force to the first pulley 36. The driving device 30 includes a drive portion 61 that can apply the rotational driving force in the forward and reverse directions and a drive transmission portion 31 that can transmit, of the rotational driving force applied from the drive portion 61, only the rotational driving force in the forward direction to the first pulley 36 of the pulley portion 28.

The drive portion 61 includes a drive source M such as a motor, a drive input gear 49 that is fed with the rotational driving force from the drive source M, and a drive shaft 50 that protrudes from the drive input gear 49 inward in the axial direction (toward the pulley portion 28). The drive shaft 50 is located coaxially with the first pulley 36.

The drive transmission portion 31 is disposed between the drive input gear 49 and the first pulley 36 with respect to the axial direction. The drive transmission portion 31 includes a drive coupling 42 that is adjacent to an outer (driving device-side) end part of the first pulley 36 with respect to the axial direction and an urging member 43 disposed between the drive coupling 42 and the drive input gear 49 with respect to the axial direction.

The drive coupling 42 is composed of a first claw portion 44 (driven-side coupling) and a second claw portion 45 (driving-side coupling) provided side by side in the axial direction. The first claw portion 44 is a cylindrical gear that has a first gear surface 46 formed on its outer end surface in the axial direction (at the side farther from the first pulley 36). The first claw portion 44 is a member separate from the first pulley 36, and is fitted to an outer end part of the first pulley 36 in the axial direction by an engaging means, such as by snap-fitting or press-fitting, or by an adhering means, such as with adhesive.

The second claw portion 45, like the first claw portion 44, is a cylindrical gear that has a second gear surface 47 formed on its inner end surface in the axial direction (the surface facing the first gear surface 46 of the first claw portion 44). The second claw portion 45 is located outward of the first claw portion 44 with respect to the axial direction (at the drive input gear 49 side), and is supported so as to be slidable in the axial direction with respect to the drive shaft 50. The second claw portion 45 and the drive shaft 50 are restrained from rotating relative to each other in the rotation direction, and the rotational driving force from the drive input gear 49 is transmitted to the second claw portion 45. The second gear surface 47 faces the first gear surface 46 of the first claw portion 44 in the axial direction.

As shown in FIGS. 3 and 4, the first gear surface 46 and the second gear surface 47 each have a plurality of projections 48 arranged at equal intervals in the circumferential direction. The projections 48 project in the axial direction. The projections 48 each have an engagement surface 48 a that extends from the tip end of projection 48 in its projecting direction in a straight line along the axial direction and an inclined surface 48 b that is inclined such that the dimension of the projection decreases from the tip end of the projection 48 along the forward rotation direction.

The urging member 43 is located between the second claw portion 45 and the drive input gear 49 with respect to the axial direction, and is fitted outside the drive shaft 50. The urging member 43 urges the second claw portion 45 toward the first claw portion 44 with respect to the axial direction. The urging force of the urging member 43 keeps the second and first gear surfaces 47 and 46 in contact with each other.

As will be understood from FIG. 3, when the second claw portion 45 rotates in the forward direction (direction indicated by arrow C1 in FIG. 3), the engagement surface 48 a of the second gear surface 47 makes contact with the engagement surface 48 a of the first gear surface 46; thus the second and first claw portion 45 and 44 are restrained from rotating relative to each other, and the rotational driving force is transmitted from the second claw portion 45 to the first claw portion 44. Thus the first and second claw portions 44 an 45 engage (couple) with each other in the rotation direction, and the first claw portion 44 rotates in the forward direction. Here, as mentioned above, the first claw portion 44 is fixed to the first pulley 36, and thus the first pulley 36 too rotates in the forward direction.

FIG. 5 is a plan view of the first pulley 36 as seen from outward of it in the axial direction (from the driving device 30 side) as the first pulley 36 is rotating in the forward direction (counter-clockwise in the illustration).

As mentioned above, the driving device 30 transmits the rotational driving force in the forward direction from the drive input gear 49 (see FIG. 2) via the drive transmission portion 31 to the pulley portion 28. Here, if the rotational driving force in the forward direction is greater than the suspension load mentioned above, the driving device 30 rotates the first and second pulleys 36 and 37 in the forward direction (counter-clockwise in the illustration) against the rotational force that acts on them.

To the first pulley 36, one ends of the first and second wires 29 a and 29 b are fixed. Accordingly, as the first pulley 36 rotates in the forward direction, then as shown in FIG. 5 the first and second wires 29 a and 29 b are wound around the winding portion 38 of the first pulley 36. Likewise, to the second pulley 37, one ends of the third and fourth wires 29 c and 29 d are fixed. Accordingly, as the shaft 35 rotates in the forward direction and consequently the second pulley 37 rotates in the forward direction, the third and fourth wires 29 c and 29 d are wound around the winding portion 38 of the second pulley 37 (see FIG. 2). Thus the wires 29 (first, second, third, and fourth wires 29 a, 29 b, 29 c, and 29 d) are pulled up (see arrows C3 indicated by dash-and-dot lines in FIG. 5), and the sheet stacking tray 27 ascends (see FIGS. 2 and 5).

When the rotational driving force in the forward-direction (direction indicated by arrow C1 in FIG. 3) that is transmitted from the second claw portion 45 to the first claw portion 44 becomes equals to the rotational force in the reverse direction (direction indicated by arrow C2 in FIG. 3) that is ascribable to the suspension load mentioned above, that is, when the forces balance out, the first and second pulleys 36 and 37 stops rotating. Thus the wires 29 stop being wound or unwound, and the sheet stacking tray 27 stops at a predetermined ascent-descent position.

FIG. 6 is a plan view of the first pulley 36 as seen from outward of it in the axial direction (from the driving device 30 side) as the first pulley 36 is rotating in the reverse direction (clockwise in the illustration). FIG. 7 is a plan view showing a state where, with the sheet stacking tray 27 lowered to the lowest position in the ascent-descent direction, the drive portion 61 is applying a rotational driving force in the reverse direction (direction indicated by arrow C2 in the illustration) to the second claw portion 45.

When the drive portion 61 applies a rotational driving force in the reverse direction (direction indicated by arrow C2 in FIG. 3) to the second claw portion 45 and consequently the second claw portion 45 rotates in the reverse direction, the engagement surface 48 a of the second claw portion 45 moves in a direction away from the engagement surface 48 a of the first claw portion 44 with respect to the rotation direction (see FIG. 3). This cancels the transmission of the rotational driving force in the forward direction from the first claw portion 44 to the second claw portion 45. As a result, with the rotational force ascribable to the suspension load mentioned above, the first pulley 36 rotates in the reverse direction. Thus, as shown in FIG. 6, the wires 29 are unwound from the pulley portion 28 (see arrows C4 indicated by dash-and-dot lines in FIG. 6), and the sheet stacking tray 27 descends.

When the sheet stacking tray 27 descends down to its lowest position in the ascent-descent direction, the suspension load mentioned above is canceled, and the wires 29 stop being unwound. Thus the first and second pulleys 36 and 37 stops rotating in the reverse direction. In this state, as the second claw portion 45 rotates in the reverse direction, then as shown in FIG. 7 the engagement surface 48 a of the second claw portion 45 moves away from the engagement surface 48 a of the first claw portion 44. Meanwhile, the tip ends of the projections 48 of the second claw portion 45 slide on the inclined surfaces 48 b of the first claw portion 44.

Here, as mentioned above, the second claw portion 45 is pressed toward the first claw portion 44 by the urging member 43. Thus, once the projections 48 of the second gear surface 47 move over the next projections 48 downstream with respect to the rotation direction, the second claw portion 45 moves back closer to the first claw portion 44. In this way, when with the sheet stacking tray 27 lowered to the lowest position in the ascent-descent direction the second claw portion 45 rotates in the reverse direction, the second claw portion 45, while sliding in the axial direction and repeatedly moving toward and away from the first claw portion 44, rotates in the reverse direction, and the second claw portion 45 rotates idly relative to, without engaging with, the first claw portion 44. Now that, as mentioned above, the suspension load has been canceled and the wires 29 have stopped being unwound, the first and second pulleys 36 and 37 no longer rotate in the reverse direction.

As described above, owing to the first and second claw portions 44 an 45 engaging (coupling) with each other or rotating idly relative to each other, the drive transmission portion 31 transmits from the drive portion 61 to the pulley portion 28 only the rotational driving force in the forward direction and not the rotational driving force in the reverse direction.

Also if the sheet stacking tray 27 stops unintendedly, by failure or the like, midway before reaching its lowest position, the second claw portion 45 does not engage with but rotate idly relative to the first claw portion 44 as described above. Thus, also in that case, the drive transmission portion 31 does not transmit the rotational driving force in the reverse direction from the drive portion 61 to the pulley portion 28.

Referring back to FIG. 1, in an upper part of the housing 26, the sheet feed device 32 is disposed that feeds sheets P downstream in the sheet conveyance direction. The sheet feed device 32 includes a pickup roller 53, a pair of sheet feed rollers 54, a pair of conveyance rollers 62, and a sheet discharge port 51. The pickup roller 53 is located above the sheet stacking tray 27, at a position where it makes contact with the top surface of the stacked sheets P as the sheet stacking tray 27 ascends. When the pickup roller 53, in contact with the top surface of the sheets P, rotates in the feeding direction (clockwise in FIG. 1), one sheet P at the top of the stack of sheets P is fed out.

The pair of sheet feed rollers 54 are disposed opposite each other, downstream of the pickup roller 53 with respect to the sheet conveyance direction. The pair of conveyance rollers 62 are disposed opposite each other, downstream of the pair of sheet feed rollers 54 with respect to the sheet conveyance direction. The sheet discharge port 51 is located in a downstream end part of the sheet feed device 32 with respect to the sheet conveyance direction, and is open in a side surface of the housing 26. A sheet P fed downstream by the pickup roller 53 is conveyed further downstream by the pair of sheet feed rollers 54 and the pair of conveyance rollers 62, and is discharged via the sheet discharge port 51 out of the sheet storage device 20. As mentioned above, to the sheet discharge port 51, the confluence passage 52 of the image forming apparatus 1 is connected. Thus the sheet P discharged via the sheet discharge port 51 is introduced through the confluence passage 52 into the sheet feed passage 10, is then conveyed to the image forming portion 4 inside the image forming apparatus 1, and undergoes image formation as described above.

Now a description will be given of reverse winding of a wire that occurs in a conventional sheet storage device 70. For any components that find their counterparts in the construction according to the present disclosure, the same reference signs will be used and no description will be repeated. FIG. 8 is a side view showing a reference example of a wire winding mechanism in the conventional sheet storage device 70. The conventional sheet storage device 70 includes a pulley 71 that is connected to a drive source M, a sheave 41 e located above the pulley 71, and a sheet stacking tray 27 disposed below the sheave 41 a.

The pulley 71 is supported so as to be rotatable in forward and reverse directions (clockwise and counter-clockwise in FIG. 8), and one end of the wire 29 is fixed to the winding portion 38 of the pulley 71. The pulley 71 is coupled to the drive source M, and the drive source M can transmit a rotational driving force in the forward and reverse directions to the pulley 71.

Normally, as the pulley 71 rotates in the reverse direction (clockwise in the illustration), the wire 29 is unwound and the sheet stacking tray 27 descends. However, if, as shown in FIG. 8, with the wire 29 fully unwound the drive source M applies the reverse-direction (unwinding-direction) rotational driving force to the pulley 71, the point at which the wire 29 and the pulley 71 are coupled together moves to the opposite position across the winding portion 38 (moves from position A1 to position A2 in FIG. 8), that is, reverse winding occurs. If from this state the pulley 71 rotates further in the reverse direction, the wire 29 is wound around the pulley 71 (see arrows C5 indicated by dash-and-dot lines in the illustration), and thus the sheet stacking tray 27 ascends. In this way, if the pulley 71 rotates in the reverse direction with the sheet stacking tray 27 located at its lowest position in the ascent-descent direction, the sheet stacking tray 27 ascends contrary to what is expected.

By contrast, with the sheet storage device 20 according to the present disclosure, as described above, the drive transmission portion 31 transmits from the drive portion 61 to the pulley portion 28 only a rotational driving force in the forward direction, in which the wire 29 is wound, and not a rotational driving force in the reverse direction, in which the wire 29 is unwound. Thus, even if with the wire 29 fully unwound the sheet discharge port 51 applies a rotational driving force in the reverse direction to the second claw portion 45, it is not transmitted from the second claw portion 45 to the first claw portion 44, and thus the pulley portion 28 does not rotate in the reverse direction. Thus, with the sheet stacking tray 27 lowered to the lowest position in the ascent-descent direction and hence with the wire 29 fully unwound, the pulley portion 28 does not rotate in the reverse direction, and this prevent reverse winding of the wire 29. Moreover, the pulley portion 28, when it rotates, does not rub against the wire 29, and this prevents breakage in the wire 29 and the pulley portion 28. Moreover, there is no need to separately provide a detection sensor or a controlling means, and this helps suppress an increase in the manufacturing cost. It is thus possible, while suppressing an increase in cost, to provide a sheet storage device 20 that is less prone to sheet feed failure and breakage.

As described above, the winding portion 38 has a tapered outer diameter that increases toward one side in the axial direction (inward in the axial direction). Accordingly, as the wire 29 is wound around the winding portion 38, it is wound around the winding portion 38 orderly starting at an outer end part of it with respect to the axial direction. Thus, the wire 29 is wound flat throughout from an outer to an inner end part of the winding portion 38 with respect to the axial direction, and is less prone to entangling.

The embodiment specifically described above is not meant to limit the scope of the present disclosure, which thus allows for various modifications without departure from the spirit of the present disclosure. For example, while the above description deals with an example where the first claw portion 44 is a member separate from the first pulley 36, this is not meant as any limitation. Instead, for example, the first claw portion 44 may be formed simultaneously and integrally with the first pulley 36 as a single component. In that case, the first claw portion 44 protrudes from an outer end part of the first pulley 36 in the axial direction. Moreover, in that case, the second pulley 37 does not need to have a first claw portion 44 formed on it.

It is also possible to employ a construction where the first claw portion 44 is supported so as to be slidable in the axial direction, the second claw portion 45 is fixed to the drive shaft 50, and the urging member 43 is disposed between the first claw portion 44 and the first pulley 36. In that case, the urging member 43 urges the first claw portion 44 toward the second claw portion 45.

The present disclosure finds applications in large-capacity sheet storage devices that can store sheets to be supplied to an image forming apparatus. Based on the present disclosure, it is possible to suppress failure in sheet feeding from a sheet storage device to an image forming apparatus. 

What is claimed is:
 1. A sheet storage device comprising: a housing; a sheet stacking tray that is supported inside the housing so as to be ascendable and descendable and on which a sheet is stacked; a shaft that extends in a width direction of the housing and that is supported so as to be rotatable in forward and reverse directions; a first pulley that is fixed to one end of the shaft; a second pulley that is fixed to another end part of the shaft; a plurality of wires suspending the sheet stacking tray; the plurality of wires wound around the first and second pulleys as the shaft rotates in a forward direction, and unwound from the first and second pulleys as the shaft rotates in a reverse direction; and a driving device including: a drive portion that generates a rotational driving force; and a drive transfer portion that transmits the rotational driving force in a forward direction to the first pulley and that shuts off the rotational driving force in a reverse-direction, wherein the drive transfer portion includes: a driving-side coupling that is provided on a drive shaft of the drive portion so as to rotate together with the drive shaft, the driving-side coupling rotating together with the drive shaft; and a driven-side coupling that is provided on the first pulley so as to rotate together with the first pulley, the driven-side coupling being coupled to the driving-side coupling, when with the rotational driving force in a forward direction the driving-side coupling rotates in the forward direction, the driving-side coupling and the driven-side coupling couple to each other to transmit the rotational driving force in the forward-direction from the drive portion, so that the first and second pulley rotates in the forward direction with the shaft, so that the plurality of wires are wound around the first and second pulleys to lift up the sheet stacking tray, when with the rotational driving force in the reverse direction the driving-side coupling rotates in the reverse direction, the driven-side coupling with uncoupled state, by following rotation of the driving-side coupling in the reverse direction, rotate in the reverse direction, due to a weight of the sheet stacking tray the plurality of wires are unwound from the first pulley and the sheet stacking tray descends, and when the sheet stacking tray stops descending and the driven-side coupling stops rotating in the reverse direction while the driving-side coupling is rotating in the reverse direction, the driving-side coupling rotates idly relative to the driven-side coupling that has stopped.
 2. The sheet storage device according to claim 1, wherein the driving-side coupling is disposed to face the driven-side coupling on an axis of the drive shaft so as to be slidable in the direction along the axis of the drive shaft, the drive transfer portion includes an urging member that urges the driving-side coupling toward the driven-side coupling, the driving-side coupling makes contact with the driven-side coupling and rotates in the forward direction to engage with the driven-side coupling so as to transmit the rotational driving force in the forward direction of the drive portion to the first pulley.
 3. The sheet storage device according to claim 1, wherein The first and second pulleys each have a plurality of cylindrical winding portions around which the plurality of wires are wound, and the plurality of winding portions are arranged side by side in an axis direction of the drive shaft and have a tapered outer diameter that increases toward one side in the axial direction.
 4. The sheet storage device according to claim 3, wherein the plurality of wires includes: a first wire and a second wire of which one ends are fixed respectively to the plurality of winding portions of the first pulley; and a third wire and a fourth wire of which one ends are fixed respectively to the plurality of winding portions of the second pulley.
 5. The sheet storage device according to claim 1, wherein the driven-side coupling faces the driving-side coupling with respect to the direction along an axis of the drive shaft, and is formed integrally with the first pulley on an end surface of the first pulley facing the driven-side coupling.
 6. An image forming unit comprising: an image forming apparatus including an image forming portion that forms an image on the sheet; and the sheet storage device according to claim 1 including a sheet feed mechanism that is connected to the image forming apparatus and that feeds the sheet to the image forming portion. 